HIV-1 persists in patients despite years of suppressive treatment with antiretroviral therapy (ART) and results in disease relapse when treatment is interrupted. One major barrier to treatment eradication is a reservoir of latently infected CD4+ T-cells. Whether these latently infected cells give rise to low-level ongoing replication or episodically activate and produce virus is controversial but this viral persistence likely contributes to ongoing immuno-pathologic effects that include incomplete T-cell restoration and the global immune activation that are implicated in HIV associated cardiovascular, renal and hepatic disease even among those on highly active antiretroviral therapy (HAART). It has also been recently recognized that despite expressing some markers of T-cell activation, T-cells from HIV infected patients also exhibit markers of T-cell exhaustion or tolerance that may underlie the insufficiency of the immune response against HIV-1. Our work from the previous funding cycle suggests that the latent viral reservoir may be heterogeneous in composition in vivo and the molecular mechanisms underlying viral latency are likely complex. We find that both T-cells in the gut and those in the blood exhibit very low HIV expression levels despite high levels of T-cell activation. One unifying mechanism for the attenuated expression of HIV could be the T-cell exhaustion that appears to accompany HIV infection. Our preliminary data suggest that, paradoxically, after successful viral suppression on ART, the proportion of cells expressing CTLA-4, a marker of T-cell anergy, increases. In the current proposal we will investigate evolution of the cellular reservoir of virus from patients initiating therapy during chronic HIV infection by examining individual CD4 populations based on presence or absence of markers of activation and anergy. We will test the novel hypothesis that tolerance acquired as a byproduct of chronic HIV infection, attenuates viral expression and gives rise to the paradoxical retention of large numbers of cells with latent HIV infection during suppressive therapy. We will determine whether epigenetic modification of the HIV LTR coincides with epigenetic modification of promoters of genes associated with T-cell activation. Finally, we will examine the effects of agents designed to reactivate HIV from latency or that reverse T-cell anergy on virus expression from T-cells obtained from patients on suppressive therapy in order to form the foundation for future interventions to purge the latent reservoir.